Cellulose triacetate fabrics of improved safe ironing temperature and process of heat treatment to obtain said fabrics



United States Patent CELLULOSE TRIACETATE FABRICS OF IM- PROVED SAFE IRONING TEMPERATURE AND PROCESS OF HEAT TREATMENT TO OBTAIN SAID FABRICS Donald Finlayson and Boleslaw Krzesinski, Spondon, near Derby, England, assignors to British Celanese Limited, a corporation of Great Britain No Drawing. Application December 28, 1953 4 Serial No. 400,793

Claims priority, application Great Britain January 1, 1953 11 Claims. (Cl. 8-131) fabrics, can safely be ironed at temperatures up to about 240 C., at which temperature they begin to scorch, cellulose acetate fabrics as heretofore obtained are more sensitive, having a safe ironingtemperature of about l70180 C.; if this temperature is exceeded there is a risk of imparting a gloss or shine to the fabric, unless the operator is very skilful. It is an advantage of the present invention that it provides textile materials consisting of or containing cellulose acetate yarns, yet having safe ironing temperatures of at least 200 C. and in many cases 230240 C. The materials having safe ironing temperatures of 230240 C. can safely be ironed under the same conditions as cotton, linen and regenerated cellulose goods.

In describing and defining the invention, another property of cellulose acetate textile materials will be referred to, namely the sticking temperature. This is a rather more definite measure of the sensitivity to temperature ofthe material, and for the purpose of the present invention is to be taken as the lowest temperature at which a heated iron, after standing for 10 seconds on a fabric vof the cellulose acetate, causes the fabric to stick to its surface. The sticking temperature of cellulose acetate materials has, within fairly wide limits, been regarded as independent or nearly independent of the chemical composition of the cellulose acetate; for example, it is lay havinga sticking temperature in the neighbourhood of 220 to 240 C. This, We believe, is accounted for by the existence in this form of cellulose triacetate of a particular arrangement of the macro-molecules of the triacetate, involving closer or more orderly packing than is found in cellulose triacetate textile materials as previously made. This may also be expressed by terming the cellulose triacetate textile materials having a sticking temperature of 220 to 240 C. materials of cellulose triacetate of an increased degree of crystallinity, .as compared with the materials of cellulose triacetate of a normal degree of crystallinity such as are obtained, for example, directly by melt spinning or dry spinning methods, and which have a sticking temperature of about 200 C. The sticking temperature is thus seen to be not simply an arbitrary figure of practical significance, but also a function of the macro-molecular structure of physical form of the cellulose triacetate, by means of which this physical form can be defined.

The present invention thus comprises, as new products, textile materials made at least in part from thermoplastic fibres and having a safe ironing temperature of at least 200 C., whose thermoplastic content consists wholly of fibres of cellulose triacetate'which is in the physical form in which fibres thereof have a sticking temperature of at least 220 C. Preferably the cellulose triacetate has an acetyl value of 60.0-62.5% reckoned as acetic acid.

The present invention also comprises the manufacture of these new products by heating a textile material comprising, as the sole thermoplastic constituents, fibres of cellulose triacetate of a normal degree of crystallinity having a sticking temperature of about 200 C. to a raised temperature below the thermal softening temperature of the cellulose triacetate (i. e. the temperature at which it softens appreciably under the action of heat alone), the said temperature and the time of treatment being so correlated that the sticking temperature of the cellulose triacetate fibres is raised to at least 220 C.

'the' form of tops, slivers and other structures in which they 'are more or less loosely held together. The term fibres includes both continuous filaments of indefinite length and short lengths of filament such as staple fibres.

The cellulose triacetate textile material of. a normal degree of crystallinity from which the new products are obtained may with advantage be made by a meltspinning process, especially a process described in U. S. applications Ser. Nos. 243,994, filed August 28, 1951; 292,771, filed June 10, 1952, now abandoned; 292,772, filed June 10, 1952; 304,441, filed August 14, 1952, now abandoned; 338,834, filed February 25, 1953; or in U. S. application Ser. No. 423,743, filed April 16, 1954. In one such process a powdered cellulose. ester is urged (e. g. by a rapidly reciprocating tamper) against the side of a heated plate havingspinning orifices therein,- the powdered ester is fused by the heat applied to the plate, the fused ester is drawn away from the orifices in the form of filaments, and fresh-powdered ester is ,continuously fed to the plate. The spinning orifices may be circular, or they may be in the form of slits or of two I or more closely spaced or intersecting holes, as described 3 in U. S. application Ser. No. 338,834, filed February 25, 1953. In another process cellulose triacetate in the form of a coherent rod or a block or tablet of uniform crosssection is pressed axially against a heated plate having spinning orifices therein. The cellulose triacetate may contain pigments, dyes or other effect materials, as described for example in U. S. application Ser. No. 292,771, filed June 10, 1952, now abandoned. Wet and dry spinning methods may also be used to form the cellulose triacetate textile materials. Thus solutions of cellulose triacetate in mixtures of methylene or ethylene chloride with methyl or ethyl alcohol or acetic acid, or in acetic acid alone, may be extruded as filaments and set either by means of a coagulating liquid or by an evaporative method. For example solutions of cellulose triacetate in mixtures of methylene or ethylene chloride with acetic acid may be extruded into a coagulating liquid comprising an aqueous alcohol, especially aqueous ethyl alcohol of concentration about 90-95%, as described in U. S. application Ser. No. 184,102, filed September 9, 1950, now Patent No. 2,657,973 or solutions in acetic acid may be extruded into aqueous acetic acid which may with advantage contain a fairly high proportion of ammonium or an alkali metal acetate, an alkaline earth metal acetate or magnesium acetate, or of some other salt.

Yet another method by which textile materials of cellulose triacetate of a normal degree of crystallinity may be obtained is the further acetylation of a textile material of cellulose acetate of lower acetyl value. For instance, yarns or fabrics of acetone-soluble cellulose acetate may be further acetylated with acetic anhydride in the presence of a diluent such as benzene, and of a basic or acid esterification catalyst such as pyridine, sulphuric acid, perchloric acid or hydrochloric acid with or without a metal chloride such as zinc chloride or ferric chloride as described in British Patents Nos. 448,816, 448,817, and 448,917.

In putting the invention into practice, the textile material comprising cellulose triacetate of a normal degree of crystallinity may be heated either in the absence or in the presence of water. For example the material may be subjected to dry heat in a gaseous atmosphere, e. g. by means of a current of hot air, at a temperature between 170 and 225 C. and especially between 185 and 220 C. The higher the temperature, the shorter is the heating time needed. For example, the material may be heated to about 185 C. for minutes or more, or to about 190 C. for 5 minutes or more, while at higher temperatures still even shorter times can be employed,

down to about seconds at 220 C. Lower temperatures can be used with satisfactory results if the material is heated in the presence of wet steam or water under pressure. Thus under these conditions temperatures between about 120 C. and 160 C., and especially between 125 and 150 C., are sufficient, and the material may be heated for periods considerably less than 5 minutes, e. g. for about 5 seconds at 160 to 1-2 minutes at 120 C. It will be realised that the heating periods given above are approximate minima which should be observed if the highest possible sticking temperature and safe ironing temperature are to be achieved; they can be extended if desired, and it may be convenient to do this; if they are substantially reduced, however, the degree by which the sticking temperature and safe ironing temperature are raised will in general also be considerably reduced.

In the course of the heat treatment the textile material tends to shrink somewhat, usually by between about 1% and 3%, this shrinkage being greater at higher temperatures than at lower. The shrinkage can be prevented by keeping the material under tension, or the material may be allowed to shrink either quite freely or under some constraint, e. g. by at least half as much as it would in the complete absence of tension.

The treatment can be applied to individual batches'of material, e. g. lengths of fabric, hanks of yarn, or yarn packages (which may be loosely wound so as to permit shrinking), or continuously as to a running fabric or yarn. The heat may be applied to the material by means of a fluid heat transfer medium, e. g. hot air, dry or wet steam, hot water under pressure, a low melting alloy of the Woods metal type, or a low melting mixture of salts. (When a molten alloy or mixture of salts is used the temperature preferably does not exceed about 205 C.) Yarns and the like are usually best treated either in the form of hanks or by a continuous method, owing to the difiiculty of allowing for uniform shrinkage or maintaining uniform control over shrinkage if the yarns are in package form; for example they may be passed through wet steam or hot water in a device such as may be used for stretching acetone-soluble cellulose acetate yarns while they are softened by these media, except of course that the yarn is withdrawn from the device either at about the same speed or more slowly, instead of much more rapidly, than it enters it. Examples of heating devices that may be used will be found described in U. S. Patent No. 2,142,909 and United Kingdom Patent No. 443,773. Yarns may also be treated on thread-storage thread-advancing reels and like devices, which may be arranged to permit a degree of shrinkage.

Other means of heating may be adopted as well as or instead of contact with gaseous or liquid heat transfer media. For example, the material may be passed over heated plates or over heated rolls or other forwarding means, or it may be heated by means of radiation, as in the known types of infra-red heating devices.

It is possible to combine the treatment of the invention with a treatment to modify the appearance of a fabric, for instance by heating the fabric by pressing against it a polished or engraved plate at the desired temperature, so imparting to the fabric a glazed or patterned appearance.

It will have been noted that, according to the particular method of heating employed, there exist upper temperature limits above which the material is preferably not heated. If these temperatures are exceeded, the materials begin to suffer an undesirably high degree of shrinkage. We have, however, found that when treat ing one particular class of cellulose triacetate material, these upper limits may if desired be exceeded by a very wide margin. This class consists of materials in which the cellulose triacetate yarns are highly orientated though still of a normal degree of crystallinity; such yarns may be obtained by stretching yarns of acetone-soluble cellulose acetate while they are in a softened condition to orientate them and so to increase their tenacity in the known way, and then subjecting these highly orientated yarns to a further acetylation in a non-solvent medium while preventing them from shrinking to any substantial degree. The resulting highly orientated cellulose triacetate yarns may be subjected to dry heat at temperatures up to about 285 C., e. g. by means of hot air or by contact with a heated surface, without shrinking unduly.

The new textile products are characterised not only by their high sticking temperature and high safe ironing temperature, but also by their good dimensional stability at high temperatures. Thus they may be heated to temperature of 230 to 235 C. and higher, without undergoing much change in dimensions, whereas cellulose triacetate materials (other than highly orientated materials as described above) which have not been given the treatment of the invention, and also materials made from acetone-soluble cellulose acetate, when heated to these temperatures undergo a very considerable degree of shrinkage, and also suffer a serious loss of strength.

The invention is illustrated by the following examples.

Example 1 A cellulose triacetate yarn was made by a melt-spin- 5 ning process as described in U. S. application Ser. No. 243,994, filed August 28, 1951', it had a filament denier of 2.4. Fabrics formed from this yarn had a safe ironing temperature of about 180 C. and a sticking temperature in the neighbourhood of 200 C. One hank of this yarn was exposed for 10 minutes to a current of air heated to 180 C., and another for 5 minutes to a current of air heated to 190-2 C., the yarns being held under conditions such that they were free to shrink. Tlie yarn which had been heated at 180 C. then had shrunk by 12%. had an unchanged tenacity and had shrunk by 23%. In both cases a fabric woven from the treated yarn had a safe ironing temperature of about 235 C., i. e. of the same order as the safe ironing temperature of cellulose fabrics such as cotton and linen.

The treated yarns had also a high degree of dimensional stability. Thus the yarn heated at 190200 C. suffered no further shrinkage when subsequently heated to 235 C. for 1 minute; moreover after this further heating its tenacity and extension at break were practically unchanged. When the untreated yarn was heated to 235 C. for 1 minute it shrank by 23% and its tenacity and extension at break fell.

Example 2 A fabric woven from a yarn of cellulose triacetate of acetyl value about 61.5% reckoned asacetic acid, made by a melt-spinning process and having a safe ironing temperature of about 180 C. was held on a stenter while air at a temperature of 215 to 220 C. was blown onto it from both sides for 20 seconds. After this treatment, the fabric had a safe ironing temperature of 240 C.

Example 3 Lengths of a fabric woven from yarns of cellulose triacetate of acetyl value 61.5 made by a melt spinning process and having a safe ironing temperature of about 180 C., were immersed in molten Woods metal at 190 C. for 10 minutes and at 200 C. for minutes respectively. In both cases the safe ironing temperature of the fabric was raised to 220 C.

Example 4 A fabric woven from yarns of cellulose triacetate, of acetyl value about 61.0%, made by a melt-spinning process and having a safe ironing temperature of 180 C. was placed in a pressure vessel full of water and provided with an open steam coil. The temperature of the water was raised rapidly to about 130 C. by passing steam through the coil at a pressure of about 26 p. s. i. g. and the water was kept at this temperature for 1 minute. Another piece of this fabric was given the same treatment except that the temperature was raised to about 145 C. by means of a steam pressure of 40 p. s. i.,g. for about 30 seconds. In both cases the pressure was released and the fabric removed after the period sepecified. Both pieces of fabric had their safe ironing temperature raised to 240 C.

Example 5 A fabric woven from melt-spun cellulose triacetate yarn (acetyl value about 61.5 and having a safe ironing temperature of 180 C. was treated with wet steam at a pressure of 30 p. s. i. g. for 20 seconds; another length of the same fabric was treated at a steam pressure of 50 p. s. i. g. for seconds. Both treatments raised the safe ironing temperature of the fabric to 230-240 C. The treated fabrics were slightly softer in handle than similar fabrics whose safe ironing temperature had been raised in the same degree by heating to about 200 C. in a current of hot air.

The yarn heated to 190200 C.

Example 6 V i The treatments of Examples 24 were applied to a Example 7 I ,e

A denier, 60 filament cellulose acetate yarn, ob-

tained by stretching a yarn of an acetone-soluble cellulose acetate of acetyl value about 53.5% to about 10 times its original length while it was softened by means 'of wet steam under pressure, was further acetylated by means of a mixture of equal parts of benzene and acetic anhydride containing perchloric acid as catalyst. During this acetylation the yarn was held under tension so as to prevent it shrinking. The cellulose triacetate yarn so obtained was then heated for 1 minute to 280 C. During this heat treatment, the yarn shrank by about 1%. The treated yarn had a safe ironing temperature of about 240 C.

Having described our invention what we desire to secure by Letters Patent is:

1. Textile fabrics comprising thermoplastic fibres, said fabrics being capable of being ironed safely at a temperature between 220 and 240 0., all the said thermoplastic fibres consisting of a cellulose triacetate of acetyl value above 59% reckoned as acetic acid, said cellulose triacetate being in that crystalline state in which fibres thereof have a sticking temperature of about 220240 C.

2. Textile fabrics according to claim 1, wherein the cellulose triacetate has an acetyl value of 60.062.5% calculated as acetic acid.

3. Textile fabrics according to claim 2, and made wholly of cellulose triacetate.

4. Process for the manufacture of textile fabrics comprising thermoplastic fibres yet capable of being ironed safely at temperatures between 220 and 240 C., which comprises heating a fabric comprising thermoplastic fibres all of which consist of a cellulose triacetate of acetyl value above 59% reckoned as acetic acid, the said cellulose triacetate being in that crystalline state in which fibres thereof have a sticking temperature of about 200 C., to a temperature between and 285 C. at least until the cellulose triacetate has been converted into that crystalline state in which fibres thereof have a sticking temperature of about 220240 C., the tension on the fabric during the said heating being at most at a value at which the dimensions of the fabric are substantially constant during said heating.

5. Process according to claim 4, wherein the textile fabric is heated by means of wet steam at a temperature between 120 and C.

6. Process according to claim 4, wherein the textile fabric is heated by means of water at a temperature between 120 and 160 C.

7. Process according to claim 4, wherein the cellulose triacetate fibres have been made by further acetylating fibres of an acetone-soluble cellulose acetate which have been stretched in a softened condition to increase their tenacity, while avoiding substantial shrinkage of the stretched fibres, and the product is subjected to dry heat at a temperature between 185 and 285 C.

8. Process according to claim 4, wherein the cellulose triacetate has an acetyl value of 60.0-62.5 calculated as acetic acid.

9. Process according to claim 4, wherein the textile fabric is subjected to dry heat at a temperature of 225 C.

10. Process according to claim 9, wherein the textile fabric is heated by-means of a current of hot gas.

11. Process according to claim 9, wherein the textile 7: 8 alloys and molten mixtures Of'f'SfilfS at a temperature FOREIGNPATENTS' between and 205C 570,588 Great Brit ain-" 1 fi July-13,' 1945' ReferencesCitedin'thefile of this patent 7 OTHER REFERENCES UNITED STATESPATENTS 5 Work: Textile Research Jour., vol. 19,Iuly 1949,"pp. 1,959,350.. Ellis 3 May 22, .1934 381-389. 1,986,945 Schwartz et a1. Jan.i8, 1935 Ott,Emil:High"Polymers, vol. 5,'CellIilose'and Cellu- 2,092,477 Scott Sept. 7, 1937 lose Derivatives, 1946,1313. 228-232.

2,198,660 Dreyfus Apr. 30, 1940 Prestonet 31.: J our. of the Soc. of Dyers and Colorists'; 2,217,113 Hardy" Oct. 8, 1940 10 June31953, pp. 201 and 202'. 2,313,173 Schneider et'al. Mar; 9, 1943 2,563,394 Cadgene" Aug. 7, 1951 

1. TEXTILE FABRICS COMPRISING THERMOPLASTIC FIBERS, SAID FABRICS BEING CAPABLE OF BEING IRONED SAFELY AT A TEMPERATURE BETWEEN 220* AND 240*C., ALL THE SAID THERMOPLASTIC FIBERS CONSISTING OF A CELLULOSE TIACETATE OF ACETYL VALUE ABOVE 59% RECKONED AS ACETIC ACID, SAID CELLULOSE TRIACETATE BEING IN THAT CRYSTALLINE STATE IN WHICH FIBERS THEREOF HAVE A STICKING TEMPERATURE OF ABOUT 220*-240*C.
 4. PROCESS FOR THE MANUFACTURE OF TEXTILE FABRICS COMPRISING THERMOPLASTIC FIBERS YET CAPABLE OF BEING IRONED SAFETLY AT TEMPERATURE BETWEEN 220* AND 240*C., WHICH COMPRISES HEATING A FABRIC COMPRISING THERMOPLASTIC FIBERS ALL OF WHICH CONSIST OF A CELLULOSE TRIACETATE OF ACETYL VALUE ABOVE 59% RECKONED AS ACETIC ACID, THE SAID CELLULOSE TRIACETATE BEING IN THAT CRYSTALLINE STAGE IN WHICH FIBERS THEREOF HAVE A STICKING TEMPERATURE OF ABOUT 200* C., TO A TEMPERATURE BETWEEN 120* AND 285*C. AT LEAST UNTIL THE CELLULOSE TRIACETATE HAS BEEN CONVERTED INTO THAT CRYSTALLINE STATE IN WHICH FIBERS THEREOF HAVE A STICKING TEMPERATURE OF ABOUT 220*-240*C., THE TENSION ON THE FABRIC DURING THE SAID HEATING BEING AT MOST AT A VALUE AT WHICH THE DIMENSIONS OF THE FABRIC ARE SUBSTANTIALLY CONSTANT DURING SAID HEATING. 